Purification method of shellfish

Abstract

The invention discloses a shellfish purification method, and belongs to the technical field of aquatic product processing. The method comprises the following steps: firstly, establishing an optimal purification environment by systematically optimizing key parameters such as water temperature, salinity, dissolved oxygen, water velocity and shellfish-water ratio; then optimized ultrasonic treatment and pulsed magnetic field treatment are adopted for synergistic bacterium reduction, in order to further improve the effect, 0.1-2.0% (w / v) of chitosan can be added into the purified water body, and the chitosan and a physical field technology generate a synergistic interaction effect. According to the method, the sand content of the shellfish can be reduced from 5% to 0.65% within 24 hours, the killing rate of pathogenic bacteria exceeds 99.5%, the shelf life of the shellfish can be prolonged from 3 days to 7 days or above through the ultrasonic-magnetic field coupling technology or by combining chitosan on the basis of coupling, the commodity percent of pass, the food safety and the commercial value of products are remarkably improved, and the method is suitable for popularization and application. And a complete and efficient shellfish purification and preservation solution is formed.

Description

Technical Field

[0001] This invention relates to the field of aquatic product processing technology, and in particular to a method for purifying shellfish. Background Technology

[0002] Shellfish have a natural filter-feeding habit, which easily accumulates silt, organic debris, and pathogenic microorganisms in the water, thus becoming a potential source of foodborne diseases. Traditional shellfish purification usually uses the clean seawater temporary holding method, which utilizes the shellfish's own metabolism and excretion to release and dilute pollutants. However, this method has the following shortcomings: (1) The purification cycle is long, usually requiring more than 24–48 hours, which increases the turnover time of the aquaculture farm; (2) It occupies a large amount of water resources, and the cost of water circulation and water quality maintenance is high; (3) The effect on removing stubborn silt and some pathogenic microorganisms is limited, and the purification effect is unstable.

[0003] To improve purification efficiency, existing technologies have incorporated several physical or chemical methods. While chemical disinfectants (such as chlorine-based agents and ozone) have some antibacterial efficacy, they are prone to leaving chemical residues, which may affect the flavor and safety of shellfish and have potential negative environmental impacts. Regarding physical methods, ultraviolet irradiation alone has limited penetrating power and is insufficient to fully inactivate microorganisms hidden in the gills and digestive tract of shellfish. Ultrasonic waves alone can remove sediment and break down some bacterial cells through cavitation effects, but improper parameter control may damage shellfish tissue, reducing survival rate and quality, and its antibacterial effect against pathogens is insufficient. While magnetic field treatment alone, especially pulsed magnetic fields, is believed to inhibit microbial activity by altering the permeability of microbial cell membranes, its overall effectiveness still needs improvement when used alone.

[0004] Therefore, there is an urgent need for a new purification method that has a shorter processing time, lower water consumption, higher removal rate of sediment and pathogens, and a positive impact on the physical quality and storage stability of shellfish, while minimizing chemical residues and environmental impact, and ensuring food safety and consistent flavor characteristics. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a method for purifying shellfish. By setting appropriate purification conditions, such as water temperature, salinity, oxygen content, and water flow rate, the method achieves the technical effect of high survival rate and low sand content of purified shellfish. Simultaneously, by employing ultrasonic treatment, pulsed magnetic field treatment, or a combination of ultrasonic and pulsed field, the method achieves efficient and rapid purification and sterilization of shellfish, while also improving the storage quality of shellfish products.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for purifying shellfish involves placing the shellfish to be purified in a purified water body. The purification conditions are as follows: water temperature of 10-20℃, salinity of 25-35‰, oxygen content of 6-8 mg / L, water flow velocity of 0.05-0.2 m / s, and shellfish to water volume ratio of 1:5-1:10.

[0007] Preferably, the purification conditions are: water temperature of 15℃, salinity of 25‰, oxygen content of 6 mg / L, water flow velocity of 0.1 m / s, and shellfish to water volume ratio of 1:5.

[0008] Preferably, the process further includes ultrasonic treatment, wherein the intensity of the ultrasonic treatment is 15~35 W / cm², and the treatment time is 3~10 minutes.

[0009] Preferably, the intensity of the ultrasonic treatment is 25 W / cm², the treatment time is 5 minutes, and the ultrasonic mode is 2 min / 2 min intermittent ultrasound.

[0010] This invention optimizes ultrasonic treatment parameters based on a balance between cavitation effect and shellfish biocompatibility. Ultrasonic intensity is the key driving force for inducing cavitation. Intensity that is too low (e.g., <15 W / cm²) fails to generate sufficient cavitation bubbles and collapse energy, resulting in insufficient removal of firmly attached mud and biofilm from shellfish surfaces and limited damage to microorganisms. Intensity that is too high (e.g., >35 W / cm²), while enhancing physical cleaning and sterilization, generates intense cavitation and strong shearing forces that irreversibly damage soft tissues such as the adductor muscle and gill filaments, leading to a significant decrease in survival rate and quality deterioration. Through systematic experiments, this invention has found that an intensity of 25 W / cm² is the optimal balance point for achieving efficient purification and a high survival rate (>98.5%). It ensures a moderate cavitation effect, effectively dislodging mud and sand, breaking up bacterial biofilms, and physically damaging microbial cells without damaging shellfish tissue. The introduction of intermittent mode further ensures biosafety, providing a window for shellfish to recover from ultrasonic stress and avoiding cumulative damage caused by continuous energy input.

[0011] Preferably, after the shellfish are purified in the purified water, they are treated with a pulsed magnetic field. The magnetic field strength of the pulsed magnetic field treatment is 2~4T, the pulse period is 10~50 ms, and the treatment time is 10~20 minutes.

[0012] Preferably, the magnetic field strength of the pulsed magnetic field treatment is 3T, the pulse period is 20 ms, and the treatment time is 15 minutes.

[0013] The core of this invention lies in the setting of pulsed magnetic field parameters, which utilizes its non-thermal biological effects to target microorganisms. The magnetic field strength determines the magnitude of the Lorentz force and induced electromotive force acting on microbial cells. If the strength is too low (e.g., <2T), it is difficult to induce a transmembrane potential across the microbial cell membrane sufficient to alter its permeability and interfere with ion channel function; if the strength is too high (e.g., >4T), although it may enhance the effect, the equipment cost and energy consumption increase dramatically, and there may be unknown biological risks. The preferred strength of this invention, 3T, has been experimentally proven to effectively interfere with the membrane potential and metabolic enzyme activity of common aquatic pathogens such as Vibrio parahaemolyticus and Escherichia coli, leading to cell leakage and death, while having no observable negative impact on macroscopic organisms like shellfish. The optimization of the pulse period aims to match the capacitance charging and discharging relaxation time of the microbial cell membrane, allowing for efficient absorption of electromagnetic energy and avoiding potential cell adaptation under continuous magnetic fields, thereby achieving higher energy utilization efficiency and sterilization effect through a "burst" mode.

[0014] Preferably, after the shellfish are purified under the following conditions: water temperature of 15℃, salinity of 25‰, oxygen content of 6 mg / L, water flow velocity of 0.1m / s, and shellfish to water volume ratio of 1:5, they are then subjected to ultrasonic treatment. The ultrasonic treatment intensity is 25 W / cm², the treatment time is 5 minutes, and the ultrasonic method is 2 min / 2 min intermittent ultrasonic treatment. Simultaneously or after the ultrasonic treatment, pulsed magnetic field treatment is performed. The magnetic field intensity of the pulsed magnetic field treatment is 3T, the pulse period is 20 ms, and the treatment time is 15 minutes.

[0015] The ultrasonic treatment and pulsed magnetic field treatment are carried out during the temporary holding and purification process of shellfish. The two can be carried out simultaneously or in any order.

[0016] Preferably, chitosan at a mass-volume ratio of 0.1 to 2.0% (w / v) is added to the purified water.

[0017] Preferably, chitosan at a mass-volume ratio of 0.8% (w / v) is added to the purified water.

[0018] The chitosan can produce a synergistic effect with the ultrasound-magnetic field combined technology, which can significantly improve the sterilization rate and extend the shelf life without affecting the survival rate of shellfish.

[0019] The effective effects of this invention are as follows: 1. This invention constructs an optimal environment for shellfish physiological activity by synergistically optimizing key parameters such as water temperature, salinity, dissolved oxygen, water flow velocity, and shellfish-to-water ratio. This shortens the purification cycle by 30%-50% compared to traditional methods (reducing sand content from 5% to below 1.5% within 24 hours), stabilizes the survival rate at over 97%, and achieves a sediment removal rate of over 90%. This parameter system provides clear preliminary experimental conditions for the subsequent optimization of ultrasonic and pulsed magnetic field treatment conditions, laying a crucial scientific foundation and providing clear guidance.

[0020] 2. The ultrasonic treatment method provided by this invention, by adjusting the purified water under specific parameters, can achieve a significant reduction in bacteria count of up to 99% against various pathogenic bacteria such as Vibrio parahaemolyticus and Salmonella without significantly affecting the survival rate of shellfish. This method utilizes the ultrasonic cavitation effect to directly destroy the microbial cell structure, acting rapidly and leaving no chemical residue, thus providing a highly efficient and safe physical sterilization method for shellfish purification.

[0021] 3. The pulsed magnetic field treatment method provided by this invention, by treating the purification system under optimized parameters, exhibits a sterilization effect of over 99% against various pathogenic bacteria such as Vibrio parahaemolyticus and Salmonella. This technology utilizes specific electromagnetic field effects to interfere with the physiological functions of microorganisms, has strong penetration, and provides uniform treatment. It can complement ultrasonic treatment, providing key technical support for constructing a comprehensive, thorough pathogenic microorganism removal system.

[0022] 4. The ultrasound-pulsed magnetic field combined technology provided by this invention produces a significant synergistic effect of "1+1>2". Its most prominent beneficial effect is that it greatly improves the storage quality and commercial value of purified shellfish. Under optimal aquatic environmental parameters, it creates a purification foundation for shellfish with high survival rate and high physiological activity. On this basis, the introduction of ultrasound and pulsed magnetic field treatments respectively achieves highly efficient targeted sterilization of pathogenic bacteria, forming a complementary physical sterilization system. Finally, by integrating the advantages of the first three parts and innovating, the synergistic use of ultrasound and magnetic field not only achieves a microbial removal effect that surpasses that of single technologies in the purification stage, but more importantly, it stimulates the quality potential of the shellfish themselves, enabling them to exhibit superior quality during storage, such as doubled shelf life, good texture retention, and significantly reduced flavor loss. This forms a complete technical closed loop from basic purification to quality improvement, completely solving the industrial dilemma of traditional methods in balancing efficiency, safety, and preservation.

[0023] 5. As a preferred synergistic effect of the present invention, when chitosan is added to the purified water, it can form a "physical-biological" synergistic sterilization system with the combined use of ultrasound and pulsed magnetic field technology, producing a synergistic effect of "1+1+1>3". Under the action of ultrasonic cavitation, chitosan can more easily contact and destroy the cell membrane of microorganisms. After being enhanced by pulsed magnetic field, it can achieve near-complete elimination of pathogenic bacteria (bacterial reduction rate >99%), and further extend the shelf life to 8 days. At the same time, it exhibits a superior ability to maintain texture, water retention and sensory quality. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Figure 1 This is a graph showing the survival rate of shellfish under different water temperatures.

[0026] Figure 2 This is a graph showing the relationship between the sand content of shellfish under different water temperatures.

[0027] Figure 3 This is a graph showing the survival rate of shellfish under different salt concentrations.

[0028] Figure 4 This is a graph showing the relationship between sand content in shellfish under different salt concentrations.

[0029] Figure 5 This is a graph showing the survival rate of shellfish under different oxygen levels.

[0030] Figure 6 This is a graph showing the relationship between sand content in shellfish under different oxygen levels.

[0031] Figure 7 This is a graph showing the survival rate of shellfish under different water flow velocities.

[0032] Figure 8 This is a graph showing the relationship between the sand content of shellfish under different water flow velocities.

[0033] Figure 9 This is a graph showing the survival rate of shellfish under different shellfish-to-water ratios.

[0034] Figure 10 This is a graph showing the relationship between the sand content of shellfish under different shellfish-to-water ratios. Detailed Implementation

[0035] To better understand the present invention, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. However, those skilled in the art will understand that the following embodiments are not intended to limit the scope of protection of the present invention, and any changes and variations made on the basis of the present invention are within the scope of protection of the present invention.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0037] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0038] Example 1: The Influence of Water Conditions on Shellfish Purification Rate Fresh shellfish were placed in a purification tank. Five temperature gradients were initially set: 5℃, 10℃, 15℃, 20℃, and 25℃. At temperatures below 5℃, the shellfish entered a dormant state, barely opening to filter feed or excrete, resulting in a very slow or even completely stopped purification process. At temperatures above 20℃, the shellfish were under stress and may close their shells, ceasing filtration and excretion, thus hindering the effective purification (sand and bacteria removal) process. Based on this, salinity gradients of 15‰, 20‰, 25‰, 30‰, and 35‰ were configured. At low salinity (below 15‰), the shellfish closed their shells due to stress, resulting in a low sand removal rate; at high salinity (above 35‰), sand removal was rapid initially but may slow down later due to decreased vitality. Dissolved oxygen concentrations were controlled at four gradients of 2, 4, 6, and 8 mg / L using an oxygen pump and dissolved oxygen meter, aiming to cover the entire range from hypoxic stress to supersaturation. The water flow velocity was adjusted to four gradients (0, 0.05, 0.1, and 0.2 m / s) using a circulating water pump. This aimed to systematically cover the complete action spectrum from still water sedimentation to water scouring, thereby accurately identifying the critical point of optimal flow velocity that balances efficient sand removal with the physiological adaptability of shellfish. Shellfish were grouped into four groups in the water tank at shellfish-to-water ratios of 1:2, 1:5, 1:8, and 1:10. These four ratios were designed to systematically examine the complete range from high-density stress to low-density relaxation, thereby accurately identifying the optimal balance point that simultaneously considers purification efficiency, shellfish survival rate, and economic benefits. Finally, samples were taken at 0, 12, 24, 36, and 48 hours, with three parallel samples from each group. Sand content was determined by gravimetric analysis, and survival rate was statistically analyzed by vitality observation. The optimal process conditions were ultimately determined through systematic comparison. Results are as follows: Figure 1 , 2 As shown in Figures 3, 4, 5, 6, 7, 8, 9, and 10, the survival rate of shellfish purified by this method is as high as 97% or above under the conditions of water temperature of 15℃, salinity of 25‰, dissolved oxygen of 6 mg / L, water flow velocity of 0.1 m / s, and shellfish-to-water ratio of 1:5. The sand content is reduced from 5% to 0.65%, which greatly improves the marketability and commercial value of shellfish, and at the same time significantly improves the production efficiency and economic benefits of the purification process.

[0039] Example 2: The sterilization effect of ultrasonic treatment on shellfish purification The shellfish to be purified were placed in a constant-temperature purification tank. The water conditions were selected from the optimal scheme in Example 1. The ultrasonic intensity gradient was set to 5, 15, 25, and 35 W / cm², and treatment was performed for 1, 3, 5, 10, and 20 minutes, respectively. Continuous ultrasound and intermittent ultrasound (with four working-intermittent cycles: 2 min / 2 min, 3 min / 3 min, 5 min / 5 min, and 10 min / 10 min) were compared. The short cycles of 2 min / 2 min and 3 min / 3 min were used to verify the potential advantages of high-frequency intermittent ultrasound in maintaining cavitation activity and maximizing biocompatibility. The long cycles of 5 min / 5 min and 10 min / 10 min were used as a comparison to explore the attenuation trend of the effect when the cycle was extended to near continuous operation. Each experiment had three parallel samples. Immediately after treatment, samples were taken to determine the total bacterial count and the number of pathogenic bacteria, and the survival rate of the shellfish was counted. The optimal ultrasonic treatment scheme was determined by comparing the sterilization effect under different parameter combinations. The results are shown in Tables 1, 2, and 3. It can be seen that under an ultrasonic intensity of 25 W / cm², a duration of 5 minutes, and intermittent ultrasonication of 2 min / 2 min, the pathogenic bacteria can be effectively eliminated (bacterial reduction rate >99%), breaking through the technical bottleneck of traditional purification technology that makes it difficult to balance bacterial reduction efficiency and biosafety.

[0040]

[0041]

[0042]

[0043] Example 3: The sterilization effect of magnetic field treatment on purified water Shellfish to be purified were placed in a pulsed magnetic field treatment device. The magnetic field strength gradients were set to 1, 2, 3, and 4 T; the pulse period gradients were 10, 20, 50, and 100 ms; and the treatment time gradients were 5, 10, 15, 20, and 30 min. Three parallel samples were set for each experiment. Immediately after treatment, samples were taken to determine the total bacterial count and the number of specific pathogens, and the shellfish survival rate was recorded. The optimal magnetic field treatment scheme was determined by comparing the microbial inactivation effects under different parameter combinations. The results are shown in Tables 4, 5, and 6. It can be concluded that the pulsed magnetic field with an intensity of 3 T, a period of 20 ms, and a treatment time of 15 min has the best bactericidal effect, achieving broad-spectrum and highly efficient removal of pathogens with a kill rate exceeding 99.2% while causing almost no damage to the shellfish (survival rate >99.5%). Meanwhile, ultrasound has a stronger physical destructive force on bacteria. This discovery provides a strong theoretical basis and huge synergistic potential for subsequent ultrasound-magnetic field combined use. Their combined use is expected to achieve comprehensive and thorough removal of all types of pathogenic microorganisms.

[0044]

[0045]

[0046]

[0047] Example 4: Effects of combined ultrasound and magnetic field therapy on the storage quality of purified shellfish and its synergistic effect. This embodiment aims to investigate the effect of ultrasound-magnetic field combined with chitosan synergist on the storage quality of purified shellfish. Shellfish samples purified under optimal water conditions (same as in Example 1) were divided into six groups: untreated control group, ultrasound-only group, magnetic field-only group, ultrasound-magnetic field combined group (0.1% chitosan), ultrasound-magnetic field combined group (0.8% chitosan), and ultrasound-magnetic field combined group (2.0% chitosan). The treatment groups, namely the ultrasound-magnetic field combined group (0.1% chitosan), the ultrasound-magnetic field combined group (0.8% chitosan), and the ultrasound-magnetic field combined group (2.0% chitosan), involved placing shellfish in purified water containing chitosan at mass-to-volume ratios of 0.1% (w / v), 0.8% (w / v), and 2.0% (w / v), respectively. Subsequently, following the optimal parameters determined in Examples 2 and 3, they underwent sequential ultrasonic treatment (intensity 25 W / cm², intervals of 2 min / 2 min, total treatment time 5 minutes) and pulsed magnetic field treatment (intensity 3 T, period 20 ms, total treatment time 15 minutes). All samples were stored at 4°C, and the total bacterial count, textural properties, cooking loss rate, and sensory indicators were periodically measured. By comparing the quality degradation rate of each group during a 7-day storage period, the synergistic mechanism of this combined technology in extending shelf life and maintaining quality was systematically evaluated.

[0048] The results (see Table 7) showed that the ultrasound-magnetic field combined with chitosan exhibited a significant synergistic preservation effect. The shelf life of the shellfish in this group was extended from 3 days in the control group to 7 days, which was far superior to the single physical field treatment group (5 days). During storage, the combined treatment group was able to maintain the firmness of the shellfish most effectively, delaying softening and autolysis; its cooking loss rate was consistently the lowest throughout the storage period, indicating that this technology can better maintain the water-holding capacity of the shellfish muscle tissue and reduce juice loss; at the same time, it maintained the best sensory indicators such as color, odor, and muscle elasticity, and even after 5 days of storage, its sensory scores were still above the acceptable threshold. This invention suggests that the cavitation effect of ultrasound promotes the contact between chitosan and microorganisms, while the pulsed magnetic field further enhances its antibacterial effect. The synergy of the three not only efficiently eliminates pathogenic microorganisms, but may also significantly enhance the stability and anti-spoilage ability of shellfish during subsequent storage by stimulating their stress defense mechanisms or slightly altering their muscle protein structure.

[0049]

[0050]

[0051]

[0052] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for purifying shellfish, characterized in that, The shellfish to be purified are placed in a purification water body for purification. The purification conditions are as follows: water temperature is 10~20℃, salinity is 25~35‰, oxygen content is 6~8 mg / L, water flow velocity is 0.05~0.2m / s, and the volume ratio of shellfish to water is 1:5~1:

10.

2. The purification method according to claim 1, characterized in that, The purification conditions are as follows: water temperature is 15℃, salinity is 25‰, oxygen content is 6 mg / L, water flow velocity is 0.1 m / s, and the volume ratio of shellfish to water is 1:

5.

3. The purification method according to claim 1, characterized in that, It also includes ultrasonic treatment, wherein the intensity of the ultrasonic treatment is 15~35 W / cm², and the treatment time is 3~10 minutes.

4. The purification method according to claim 3, characterized in that, The intensity of the ultrasonic treatment was 25 W / cm², the treatment time was 5 minutes, and the ultrasonic mode was 2 min / 2 min intermittent ultrasound.

5. The purification method according to claim 1, characterized in that, After the shellfish are purified in the purified water, they are then treated with a pulsed magnetic field. The magnetic field strength of the pulsed magnetic field treatment is 2~4T, the pulse period is 10~50 ms, and the treatment time is 10~20 minutes.

6. The purification method according to claim 5, characterized in that, The magnetic field strength of the pulsed magnetic field treatment is 3T, the pulse period is 20 ms, and the processing time is 15 minutes.

7. The purification method according to claim 2, characterized in that, After the shellfish are purified in the purified water, they are then subjected to ultrasonic treatment. The intensity of the ultrasonic treatment is 25 W / cm², the treatment time is 5 minutes, and the ultrasonic method is 2 min / 2 min intermittent ultrasonic treatment. At the same time or after the ultrasonic treatment, pulsed magnetic field treatment is performed. The magnetic field intensity of the pulsed magnetic field treatment is 3T, the pulse period is 20 ms, and the treatment time is 15 minutes.

8. The purification method according to claim 7, characterized in that, Chitosan at a mass-volume ratio of 0.1-2.0% (w / v) is added to the purified water.

9. The purification method according to claim 8, characterized in that, Chitosan at a mass-volume ratio of 0.8% (w / v) was added to the purified water.

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